Preparation of stable inverse emulsions of hydroxyethyl methacrylate and their stability evaluation by centrifugal coefficient

Abstract Several inverse emulsions were prepared with different hydrophilic-lipophilic balance (HLB) values using different water/oil ratios, temperatures and monomer and emulsifier concentrations by uniform stirring for more than 30 min. The stability of inverse emulsion was characterized by centrifugal coefficient. The emulsion form, either oil/water (O/W) or water/oil (W/O) was characterized by optical microscope and conductivity measurements. The results showed that HLB value, water/oil ratio and temperature could have an effect on the emulsion stability and emulsion form. When the HLB value of emulsifier is about 8.4, the water to oil ratio is about 1:1 and the temperature is at about 25 °C, inverse emulsion in the form of water in oil (W/O) was found to be the most stable. Here, the stablilty of emulsions was studied in relation to temperature and we found that 25 °C (room temperature) is the best for obtaining the most stable inverse emulsion, which is also most suitable for the redox initiation in this system. In the present study, we showed that temperature has a significant influence on the structure morphology and stability of inverse emulsion and hence, it is necessary to select the appropriate reaction temperature for inverse emulsion polymerization. This is a novel result. A decrease of the content of hydroxyethyl methacrylate in aqueous solution with an increase of emulsifier concentration in emulsion was found to elevate the stability of inverse emulsion. The addition of trace electrolytes in the emulsion, however, led to greatly reduced stability of the inverse emulsion.